The present invention relates to an imaging apparatus.
As a background art of this technical field, there has been proposed as JP-A-2007-180892. This document discloses that “A camera provides a face detection circuit, a gamma correction control unit, and an image signal processing circuit. The face detection circuit detects a face from a received image signal to calculate a luminance-variation evaluated value at a face domain containing the detected face. The gamma correction control unit determines a gradation characteristic on the basis of the luminance variation evaluated value calculated by the face detection circuit. The image signal processing circuit then performs a gamma correction for the received image signal on the basis of the gradation characteristic determined by the gamma correction control unit.”
In these days, digital cameras used for both static and dynamic images have been widely used, so that anybody can obtain good images easily. Among the images, a most frequently imaged subject is human, therefore, the digital cameras with a face-recognition optimization function have become widespread in such a way that a human's face is recognized automatically to then optimize the setting of camera.
The above-mentioned face-recognition function incorporated into the camera collates a pattern stored in a memory of the camera in advance with an input image to then detect a domain (hereinafter, refer to “face domain”) in which the face in a screen is present. Information present in the detected face domain includes a domain position, a photometry amount, colors, etc., and an appropriate processing is performed automatically on the basis of the above-mentioned information when imaging the detected face domain. Here, the appropriate processing includes the following steps: a processing is applied such that the face domain has an appropriate luminance; the face domain is focused in priority; a white balance is adjusted to such that the face domain becomes an appropriate color; and the setting of color signal is changed to such that a developing color of skin becomes good.
Here, the technique, which automatically corrects the face domain to the appropriate luminance, is high necessity degree for users, as pointed out the first appropriate processing. A condition, in which a luminance difference between a background and a human becomes large, occurs frequently, such as backlit condition when imaging a human. In such case, the image is profoundly affected by the luminance of background, therefore, the luminance for the human sometimes become inappropriate. A manual correction can be applied to obtaining an appropriate luminance, however, it is complicated to correct it manually. Therefore, the manual correction is difficult for average users.
In contrast, the technique, in which the face domain is corrected automatically to the appropriate luminance, includes a method of varying an exposure control (appropriate control for an iris portion, a shutter, an AGC circuit (Automatic Gain Control circuit)) in response to a target exposure amount calculated from a photometrical result of the face domain. However, an exposure control value is a value for uniformly varying the luminance of an entirely acquired image, therefore, the luminance of face domain becomes appropriate, but the luminance of background becomes inappropriate to sometimes emerge a white patch and a black deficiency.
The technique, which corrects automatically the face domain to the appropriate luminance and prevents the white patch and black deficiency of the background, includes a method of varying the exposure control in response to the target exposure amount calculated from the photometry amount of face domain.
The method, which performs the exposure control in response to the information of face domain detected by the face-recognition function, includes a technique for varying the gradation characteristic by the gamma correction control, as disclosed in the JP-A-2007-180892, for example. The gamma correction control is a technique for varying the gradation characteristic of an acquired image. The above-mentioned gradation characteristic is controlled appropriately to be compatible with the luminance of face domain and the gradation of background.
The JP-A-2007-180892 discloses a technique to calculate the luminance difference in the face domain to use the gradation characteristic in response to the calculated result, so that the appropriate luminance can be obtained even though the luminance difference is present in the face domain. However, there is no disclosure for a condition which does not become an optimal exposure by performing the correction including the exposure correction for the background etc. other than the face, for such cases where a detection frame is not present in the center of face in this method when the face is directed toward the left, right, upward, and downward directions, and a face detection frame is displaced from the face position when the face moves fast.
As described above, in the human imaging, it is necessary to optimally control the exposure correction control and set the exposure control in response to the acquired image, even though the human face is directed toward not only the front direction but also the upward, downward, left and right, and oblique directions.
Further, the JP-A-2007-180892 does not disclose the exposure correction for not only the case where the face is directed toward the upward, downward, left, right, and oblique directions but also the case where the face is obstructed by the photographic subject, such as hair etc. having a different luminance from that of skin of the face domain.